Final answer:
Plasma cells are activated B cells that produce large amounts of antibodies specific to antigens. The antibodies bind to antigens and flag pathogens for destruction.
Step-by-step explanation:
Plasma cells are activated B cells that function as antibody factories, producing large amounts of antibodies specific to a particular antigen. Antibodies are large proteins that recognize and bind to antigens, which are chemical structures on the surface of pathogens. The antibodies then form antigen-antibody complexes that flag the pathogen for destruction by phagocytes.